In consultancy, market sizing is a vital skill. It's how consultants calculate growth potential. The question is also a good way to see applicants' thought processes and how they use various tools to reach an accurate number. Since this question can be difficult, especially without data and research tools, more attention should be given to the approach used, rather than the actual number. Look for answers that demonstrate quantitative and reasoning skills. What to look for in an answer:

☛ Applicant's critical thinking skills

☛ Commitment to research and data-driven approaches

☛ Ability to identify market opportunities

Within a certain market, I examine population size and the percentage of people that use the product or service. By using surveys, analyzing data and identifying key issues customers are having with the industry, I can also estimate the number of customers we could serve but simply haven't yet.